1. Field of the Invention
The present invention relates to an operation microscope, more particularly to an ophthalmologic operation microscope.
2. Description of the Related Art
Up to now, various ophthalmologic operations have been conducted. In particular, cataract operation is an example of ophthalmologic operations that have been conducted a large number of times. With respect to cataract operation conducted now, a method called a suction technique is common. The suction technique is a method of cutting the front of the capsule of a crystalline lens along the contour thereof, inserting a suction device from the cut edge, sucking the content of the whitish crystalline lens, and implanting an intraocular lens (IOL) therein in place of the sucked content.
When the suction technique is conducted, an operation microscope is used for obtaining an enlarged observation image of an eye to be operated. At this time, in order to improve the visibility of the observation image, an image of transillumination (red reflex) produced by scattering and reflecting illumination light from the operation microscope on the retina of the eye to be operated is widely utilized. In particular, when the position of the cut edge in the front of the capsule is checked in order to insert the suction device or when it is determined whether or not the content of the crystalline lens is completely sucked, the red reflex is extremely effective.
In order to obtain the red reflex suitable for an operator, various units have been proposed and executed up to now. As main examples of such units, there are “a zero-degree illumination unit” in which a deflection mirror is disposed between the right and left observation optical axes of a binocular visible operation microscope and illumination light is guided to an eye to be operated along the optical axis of an objective lens, and “a complete coaxial illumination unit” in which an illumination optical axis and an observation optical axis are aligned with each other using a half mirror. However, in the zero-degree illumination unit, a region of red reflex resulting from an observation light flux in the right is different from that in the left. Therefore, when binocular vision is conducted, there is a problem in which good fusion of the image is not obtained. In addition, in the complete coaxial illumination unit, because of a reduction in amount of observation light flux resulting from the use of the half mirror, only an entirely dark observation image can be obtained. Therefore, there is a problem in which the visibility is inferior.
Accordingly, in many of the current operation microscopes, a unit called “an angled illumination (oblique illumination) unit” for conducting illumination at a predetermined angle with respect to the optical axis of an observation system (observation optical axis) is widely employed. As a conventional operation microscope in which the angled illumination unit is employed, an operation microscope disclosed in Japanese patent No. 3008359 has been known, for example. In which, the operation microscope includes a deflection mirror for deflecting illumination light emitted from an illumination system toward an eye to be operated, and is constructed such that the deflection mirror can be moved in a direction orthogonal to an observation optical axis to change an angle of the illumination light (hereinafter, referred to as an oblique angle) with respect to the observation optical axis between 0 to 6 degrees, thereby illuminating the eye to be operated.
Also, as another example in which the angled illumination unit is employed, an operation microscope disclosed in Japanese patent laid open No. Hei 11-169383 (FIGS. 2, 4 and 5) includes a prism for deflecting illumination light emitted from an illumination optical system toward an eye to be operated and a shielding disk for blocking a part of the illumination light passing through the prism, and is constructed such that a partial area of the illumination light blocked by the shielding disk is adjusted so as to change an oblique angle with respect to an observation optical axis in the illumination light projected to the eye to be operated by switching the partial area of the illumination light. Note that, as described in the laid open No. Hei 11-169383, the angled illumination unit is generally constructed such that an oblique angle of 2 degrees for obtaining the red reflex and an oblique angle of 6 degrees for obtaining a shadow contrast can be realized. However, in a design for an actual apparatus, the oblique angle particularly for obtaining the red reflex is within a range of about ±0.5 degrees under the present conditions. In the illumination at such an angle is called “approximately coaxial illumination”. However, this can be considered as angled illumination with a very small angle.
Now, the operation microscope is generally used for not only anterior eye segment operation such as cataract operation but also for retina and vitreous body operation which is subjected to organs in a deeply inner portion of the eye. The retina and vitreous body operation is generally conducted, while, with a state in which a contact lens is in contact with the retina of the eye to be operated, a light guide (such as a fiber) for intraocular illumination is inserted into the eye and the inner portion of the eye is observed by the operation microscope. At this time, an operator needs to conduct operation while holding the light guide by one hand. Therefore, this becomes a factor that hinders the speed and the accuracy of the operation.
In order to solve such a problem, as in an operation microscope disclosed in Japanese patent laid open No. 2002-350735 (in FIGS. 5 and 10), for example, an operation microscope constructed so as to allow an operator to conduct operation with both hands has been developed. According to the structure of the operation microscope described in such laid open, a front lens is disposed between an object lens and the eye to be operated. An inverter optical element for converting an observation image sensible to the operator as an inverse image by the front lens into an elect image is provided to be insertable onto an observation optical axis. A moving direction in alignment operation by a foot switch is switched in accordance with whether or not the inverter optical element is located on the observation optical axis. In the operation microscope, illumination light is projected from the outside of the eye to be operated thereto in order to observe the inner portion of the eye to be operated through the pupil. As an oblique angle of the illumination light, an angle at which the illumination light can pass through the pupil is used.
Also, a stereoscopic microscope disclosed in Patent publication No. Hei 7-111507 (FIGS. 1 and 2) includes a stereo angle converter for changing an oblique angle of illumination light (optical main body thereof; which is also called a stereo (angle) variator). The stereo angle converter is constructed such that an optical member formed in an inverted V-shape is rotatable on an observation optical axis. The arrangement of the optical member is changed to change a stereo base of right and left axes, thereby adjusting a stereo angle of the observation light. Accordingly, even when the pupil of a patient is small, the retina can be observed.
However, in the operation microscopes using the angled illumination unit, which are described in U.S. Pat. No. 3,008,359 and patent laid open No. Hei 11-169383, the following problem emerges. That is, because an angle is provided between the illumination optical axis and the observation optical axis, a region which is not irradiated with the illumination light is caused within an observable area of the retina, and a part of the red reflex is not incident into the observation optical system. As a result, a region in which the red reflex is not obtained is caused within an observation image.
In order to cope with the problems above, an operation microscope has been proposed in which a deflection mirror for performing the angled illumination is made movable to positions symmetric with respect to an observation optical axis, and the position of the deflection mirror is shifted so as to change a region in which the red reflex can be obtained in the observation image. However, the red reflexes cannot be obtained in the entire observation image at one time. Therefore, the position of the reflection mirror needs to be shifted every time when a region in which the generation of the red reflex is desired is changed during operation, resulting that the operation microscope is not suitable in operability.
On the other hand, when the operation microscope that can be used for the retina and vitreous body operation as described in Japanese patent laid open No. 2002-350735 is used for a patient with a small pupil such as a glaucoma patient, because the observation light is blocked by the pupil, there is a case where observation cannot be sufficiently conducted. In order to avoid such a problem, in the case where the stereo variator or the like is used to narrow the stereo base, when the stereo variator and the deflection mirror are disposed in series as in the stereoscopic microscope described in Japanese patent publication No. Hei 7-111507, the observation light is easily shaded by the deflection mirror. Accordingly, there is the case where the amount of light in the periphery of the observation image becomes insufficient. In some cases, observation becomes impossible.
Also, although there is no problem in the stereoscopic microscope for examination, in the operation microscope, there is a fear that a trouble is caused on an operation because a distance from the eye to be operated to an eyepiece (operating distance) becomes longer. In other words, an operator conducts an operation while peeping through the eyepiece to observe the eye to be operated. Accordingly, the cases can be assumed where the operator has to perform an operation with his arms unnaturally reached out, or the operator's hands do not reach the eye to be operated due to his frame.